Increasing power capture from multibody wave energy conversion systems using model predictive control

A Study about Performance and Robustness of Model Predictive Controllers in a WEC System

“…Actually, several authors have developed predictive controllers for WECs [7][8][9][10][11][12][13][14][15][16][17]. These MPCs can be grouped according to the characteristics of the cost function optimized.…”

“…Although, since the last decade, more complex controllers like MPC (model predictive control) are being employed. The interest in implementing MPCs in WEC systems is motivated by the need to increase the productive/economic viability of these systems; due to the fact that these controllers allow them to minimize mechanical fatigue in their structures (limiting the operating ranges) and to focus the control strategy on the maximization of the extracted power directly.Actually, several authors have developed predictive controllers for WECs [7][8][9][10][11][12][13][14][15][16][17]. These MPCs can be grouped according to the characteristics of the cost function optimized.…”

“…On one side, in [9][10][11]13,14], a reduced model was used for the design, which did not consider the dynamics of the radiation force. Meanwhile,in [7,8,12,13,[15][16][17], such dynamics were considered in the design model. Moreover, the previous works did not consider the dynamics of the power take-off system (PTO), neither in the evaluation, nor in the design of the MPCs.…”

“…Finally, the treatment carried out in the case of non-feasibility when solving the cost functions with restrictions should be highlighted. In this aspect, the works in [9,10,13] considered a more complete approach by adding soft constrains in the case of non-feasibility.This paper analyses the main approaches of MPCs applied to PAW systems [8][9][10][11][12][13][14][15][16][17]. In addition, a new design is proposed: MPC based on a model with an embedded integrator for controllers that follow a setpoint for the speed of oscillation of the PAW.…”

“…After an exhaustive fine-tuning for all MPCs, the main contribution of this work is obtained, and an in-depth study about performance and robustness of all MPCs through simulations is carried out. The results obtained for a sea state defined by the JONSWAP spectrum [15,16] are compared with conventional controllers: I-P control and resistive damping (RD). Furthermore, the mathematical model of the WEC system is obtained using a software simulation based on the boundary element method, such as openWEC [20].The rest of the article is organized as follows: Section 2 presents the generic mathematical model of a PAW, the standard identification methodology applied in this paper and the treatment applied to the model identified for its later use in the design of the MPCs.…”